Can a 03 GMC Yukon XL transmission go into a 03 GMC envoy XL?

No, a 2003 GMC Yukon XL transmission cannot be directly swapped into a 2003 GMC Envoy XL. The two vehicles use different transmission types and configurations, as the Yukon XL is built on a full-size SUV platform, while the Envoy XL is based on a midsize SUV platform. Additionally, the electronic control systems and mounting points may differ, making the swap impractical without extensive modifications.